Hybrid permanent magnet/synchronous machines

ABSTRACT

A rotor  33, 133  for use in an electrical machine  100  having permanent magnets  34, 134  included therein, each permanent magnet  34, 134  between an adjacent pair of poles  32, 132,  wherein each adjacent pole  32, 132  has an opposite polarity. Each permanent magnet  34, 134  has a magnetization polarity on its radially-outward surface  38, 138,  and each adjacent permanent magnet  34, 134  has the opposite polarity on its radially-outward surface  38, 138 . In addition, each pair of permanent magnets  34, 134  have the same magnetic polarity on their adjacently facing surfaces. This arrangement of permanent magnets  34, 134  may be used on electrical machines  100  having either a Lundell-type rotor  33  or salient pole rotor  133 . The arrangement of permanent magnets  34, 134  increases the output power and efficiency of the electrical machine  100  while decreasing magnetic noise.

TECHNICAL FIELD

[0001] The present invention relates to rotating electrical machines andmore particularly to permanent magnet enhanced rotors for generators ofautomobiles.

Background

[0002] Alternators (generators) are used to provide electrical power forrunning accessories and to charge batteries of automobiles. Thecombination of increased electrical power demand and generally smallervehicles creates the demand for greater power output and higherefficiency without greatly increasing the size of the alternator.

[0003] In an attempt to meet all of these requirements, several knowndesigns employ a “hybrid” alternator design in which a traditionalwound-field rotor is supplemented with permanent magnets. The additionof permanent magnets increases the rotor flux, and hence power output,as compared with traditional alternators. One such design is describedin U.S. Pat. No. 4,959,577 (hereinafter the '577 patent), issued toRadomski. In this patent, permanent magnets are installed between thepole fingers of an alternator. The magnets are magnetized in atangential direction with respect to the rotor's axis of rotation. Whilethe design of the '577 patent can provide some advantages over standardLundell rotors, the tangential magnetization is believed to beinefficient because a substantial amount of the permanent magnet flux isnot directly linked with the stator windings. Such linking may providebenefits of higher electrical output and higher power density (i.e.power output per unit volume of the alternator) of the alternator.

[0004] In an attempt to directly link permanent magnet flux with thestator windings, known designs have altered the arrangement of thepermanent magnets. One such design is disclosed in U.S. Pat. No.5,965,967 (hereinafter the '967 patent), issued to Liang.

[0005] In the '967 patent, a rotor includes a field coil magneticallycoupled with a first pole piece and a second pole piece which whenenergized magnetizes the fingers of the first pole piece and second polepiece with opposite magnetic polarities. The rotor also comprises aplurality of permanent magnets, at least two disposed between each firstpole finger and an adjacent second pole finger and having aradially-outward surface and an adjacent tangentially-facing surface offirst electromagnetic polarity and having a radially-inward surface andan adjacent tangentially surface of an opposite magnetic polarity.

[0006] Although the design of the '967 patent directly links permanentmagnetic flux with the stator windings, and hence increases poweroutput, the permanent magnet arrangement may not make optimal use of thepermanent magnets. The '967 patent has two permanent magnets per rotorslot having opposite polarities. This arrangement introduces harmonicflux, which results in decreased efficiency and increased magneticnoise.

[0007] In addition, the design of the '967 patent may not be used insalient pole type synchronous machines, whose rotor poles are nottapered, because the net permanent magnet flux linking to the statorwinding is zero. The net flux linkage is zero because the permanentmagnet flux linkage produced by the permanent magnets (preferably 2magnets per rotor slot) in the same rotor slot cancels each other out.

[0008] It would therefore be desirable to increase the power output of ahybrid permanent magnet machine while increasing the efficiency anddecreasing the magnetic noise compared to known systems.

SUMMARY OF THE INVENTION

[0009] One object of the present invention is to increase the poweroutput of hybrid permanent magnet synchronous machines. A second objectof the present invention is to improve the efficiency of the hybridpermanent magnet synchronous machines. A third object of the presentinvention is to lower magnetic noise of a hybrid permanent magnetsynchronous machine.

[0010] The present invention accomplishes all three objects by providinga new arrangement of permanent magnets that can be used in either aLundell-type or salient pole-type rotor.

[0011] The present invention is a rotor for use in an electricalmachine, where the rotor has an axis of rotation and has a first andsecond pole piece, a field winding (preferably a field coil or rotorcoil) on the rotor, and a set of permanent magnets disposed between thefirst and second pole pieces. The first pole piece and second pole pieceeach has a plurality of axially-extending pole fingers. The fieldwinding is magnetically coupled with the first pole piece and secondpole piece which when energized magnetizes the first pole fingers with anorth magnetic polarity and the second pole fingers with a southmagnetic polarity.

[0012] The permanent magnets are preferably trapezoidal shaped and aregrouped into two sets. One of the first set of permanent magnets isdisposed in every other rotor slot with its radially-inward surfaceadjacent to the inner rotor portion and its side surfaces abuttingadjacent pole pieces. One of the second set of permanent magnets isdisposed within each of the other rotor slots not occupied by the firstset of permanent magnets with its radially-inward surface adjacent tothe inner rotor portion and its side surfaces abutting adjacent polepieces. Preferably, the length of each permanent magnet substantiallyextends the length of the rotor slot and the length of the adjacent polepieces that it is contained within. The first set of permanent magnetsare magnetized with its radially-outward surface having a north magneticpolarity and each side surface having the magnetic polarity of itsadjacent pole pieces. The second set of permanent magnets are magnetizedwith its radially-outward surface having a south magnetic polarity andeach side surface having the magnetic polarity of its adjacent polepiece. Each side surface of each permanent magnet preferably contactseach corresponding adjacent pole piece.

[0013] As a result of this configuration of permanent magnets, thepresent invention increases the rotor flux in two ways. First, permanentmagnet flux travels from one set of permanent magnets to the second setof permanent magnets through the air gap, thereby increasing the fluxlinkage of the stator winding which in turn increases the alternatorpower output. Second, permanent magnet flux in the rotor cancels fluxgenerated by the field current to some extent, which reduces rotor coresaturation and further increases rotor flux. Therefore, the newpermanent magnet arrangement has better permanent magnet utilization,which leads to higher electrical outputs and hence better performance.

[0014] Further, this new permanent magnet arrangement has lower harmonicfluxes than known arrangements such as the '967 patent because thepermanent magnet flux changes more gradually in space. As a result, theloss caused by harmonic flux is lower, which gives rise to higherefficiency.

[0015] Also, one embodiment of this new permanent magnet arrangement hasless magnetic noise than previous arrangements because the permanentmagnets are not in parallel with the stator slots, allowing flux in thestator teeth to vary gradually rather than abruptly and hence reducingmagnetic noise.

[0016] Other objects and advantages of the present invention will becomeapparent upon considering the following detailed description andappended claims, and upon reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017]FIG. 1 is an exploded view of the relevant components of aLundell-type rotor containing permanent magnets according to a preferredembodiment of the present invention;

[0018]FIG. 2 is a side view of a Lundell-type rotor and stator accordingto one embodiment of the present invention;

[0019]FIGS. 3 and 4 are partial views of the rotor of FIG. 2, fromopposite ends of the rotor;

[0020]FIG. 5 is a perspective view of a permanent magnet of FIG. 3;

[0021]FIG. 6 is a side cross-sectional view of the salient pole-typerotor and stator portion of hybrid permanent magnet synchronous electricmachine according to another preferred embodiment of the presentinvention;

[0022]FIG. 7 is a top view of FIG. 6; and

[0023]FIG. 8 is a side cross-sectional view of the rotor portion of FIG.6 showing the permanent magnetic fluxes and fluxes generated by therotor current.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

[0024] Referring first to FIG. 1, illustrated are the relevantcomponents of a known Lundell-type rotor according to a preferredembodiment of the present invention, including pole pieces 20 and 22 andfield coil 24. These components are fixedly mounted for rotation on ashaft 26. Pole pieces 20 and 22 each includes a disk-shaped body 28, ahub 30 and a plurality of axially-extending pole fingers 32.Collectively, the body 28 and hub 30 are referred to as the inner rotorportion (shown as 23 on FIGS. 2-4). A permanent magnet 34 is disposedbetween each of the pole fingers 32. As is typical in a Lundell-typealternator (generator), the field coil 24 is preferably driven byunidirectional current controlled by a voltage regulator (not shown)that is applied to the coil 24 through a slip ring assembly (not shown)mounted to the rotor shaft 26.

[0025] Referring now to FIGS. 2-4, a rotor 33 according to one preferredembodiment is shown. The rotor 33 includes pole pieces 20 and 22 eachincluding an inner rotor portion 23. A permanent magnet 34 is disposedbetween each adjacent set of pole fingers 32. Further, FIG. 2illustrates in cross-section a stator 40 of the electrical machine whichincludes stator windings 42. Rotor 33 and stator 40 are separated by anair gap 44.

[0026] Each permanent magnet 34 extends approximately the length of thepole finger 32 and has a radially-inward surface 36, a radially-outwardsurface 38, and two side surfaces 37A, 37B. The width of each permanentmagnet 34 is similar to the width of each rotor slot 39 created betweenpole fingers 32. The permanent magnets are disposed in the rotor slot 39so that side surface 37A of one permanent magnet 34 is adjacent to theopposite side surface 37B of the next adjacent permanent magnet 34 andso that the radially-inward surface 36 is adjacent to the field winding(shown as 24 in FIG. 1). In addition, it is preferable that eachadjacent side surface 37A, 37B contacts the pole piece 32 between them.Each permanent magnet 34 is preferably mounted to the rotor slot 39 byadhesive, mechanical coupling or by another suitable fastening method.

[0027] Magnetization polarity of permanent magnets is best described inFIGS. 3-5. Permanent magnets 34 are magnetized with a polarity that runsalong their cross sections, as is shown by the arrows on permanentmagnets 34A and 34B. Thus, for example, taking permanent magnet 34A, theradially-outward surface 38 is of north magnetic polarity (“N”), whilethe radially-inward surface 36 is of south magnetic polarity (“S”). Theopposite is true for permanent magnet 34B, where the radially-outwardsurface 38 is of south magnetic polarity and the radially-inward surface36 is of north magnetic polarity. Further, the side surfaces 37A and 37Bof adjacent permanent magnets 34A, 34B are magnetized with the samemagnetic polarity, and may be either north or south magnetic polarity.As shown in FIG. 4, side surface 37B of permanent magnet 34B andadjacent side surface 37A of permanent magnet 34A have north magneticpolarity.

[0028] Referring now to FIG. 6 and 7, a cross-sectional view of asalient pole type rotor 133 contained with a hybrid permanentsynchronous machine 100 according to another preferred embodiment of thepresent invention is illustrated. As opposed to a Lundell-type rotor, inwhich one field coil 24 is used regardless of the number of pole fingers32, the salient pole type rotor 133 is characterized by an equal numberof rotor coils 124 and poles 132.

[0029] In FIGS. 6 and 7, the hybrid permanent magnet synchronous machine100 contains a salient pole rotor 133 fixedly mounted on a shaft (notshown) and contained within a stator core 112. The rotor 133 also has aplurality of poles 132 spaced around the outer perimeter of its innerrotor portion 123. The rotor 133 also has a rotor coil 124 which can beexcited to produce a magnetic field whenever current is applied throughslip rings (not shown) on the shaft by known methods. The rotor coils124 are configured such that each adjacent pole 132 has an oppositepolarity on its outer perimeter whenever current is applied. Asillustrated in FIGS. 6-8, pole piece 132A is designated with northmagnetic polarity, and pole piece 132B is designated with south magneticpolarity. The stator core 112 has a plurality of stator windings 116contained within slots 118 on the stator core 112 to generate outputwhenever an excitation current is applied to the rotor coils 124 and therotor 133 is driven by a driver (not shown), such as an engine.

[0030] Disposed between each adjacent pole finger 132 is a permanentmagnet 134. Each permanent magnet 134 is preferably mounted to its twoadjacent poles 132 by adhesive or by another suitable fastening method.Each permanent magnet 134 extends approximately the length of the polefinger 132 and has a radially-inward surface 136, a radially-outwardsurface 138, and two side surfaces 137A, 137B. The width of eachpermanent magnet 134 is similar to the width of each rotor slot 139created between poles 132. The permanent magnets are disposed in therotor slot 139 so that side surface 137A of one permanent magnet 134A isadjacent to the opposite side surface 137B of the next adjacentpermanent magnet 134B and so that the radially-inward surface 136 isadjacent to the rotor coil 124. Preferably, side surfaces 137A and 137Bon adjacent permanent magnets 134A, 134B are both in contact with theircommon pole 132.

[0031] The permanent magnets 134 are magnetized similarly as describedabove in FIGS. 3-5. The radially-outward surface 138 of every otherpermanent magnet 134A is of north magnetic polarity, while theradially-inward surface 136 is of south magnetic polarity. The oppositeis true for permanent magnet 134B, where the radially-outward surface138 is of south magnetic polarity and the radially-inward surface 136 isof north magnetic polarity. Further, the side surfaces 137A and 137B ofadjacent permanent magnets 134A, 134B are magnetized with the samemagnetic polarity as the pole 132 they both abut. As illustrated in FIG.6, side surfaces 137A, 137B located adjacent to pole piece 132B havesouth magnetic polarity. It is also contemplated that side surfaces137A, 137B could have north magnetic polarity while located adjacent topole piece 132A.

[0032] Referring now to FIG. 8, an illustration of the permanent magnetflux 195 and the flux 185 generated by rotor current is shown accordingto the present invention.

[0033] Permanent magnet flux 195 developed by each permanent magnetflows from the north magnetic pole of permanent magnet 134A, through theair gap 144 and stator 112. The permanent flux flows back through theair gap 144 and returns to the south magnetic pole of permanent magnet134B. The permanent magnet flux 195 then flows from the north pole ofpermanent magnet 134B, through the pole piece 132A and into the innerrotor portion 123. The permanent magnet flux then flows through polepiece 132B and returns to the south magnetic pole of permanent magnet134A. The permanent magnetic flux path 195 is illustrated for only oneset of magnets 134A, 134B, in FIG. 8; however, it is apparent that theflux path 195 is the same for all six sets of magnets.

[0034] A second permanent magnet flux 205 developed by each permanentmagnet flows from the north magnetic pole of permanent magnet 134A,through the air gap 144 and stator 112. The permanent flux flows backthrough the air gap 144 and returns to the south magnetic pole ofpermanent magnet 134B. The permanent magnet flux 205 then flows from thenorth pole of permanent magnet 134B, through the pole piece 132A andinto the inner rotor portion 123. The permanent magnet flux then flowsthrough pole piece 132B and returns to the south magnetic pole ofpermanent magnet 134A. The permanent magnetic flux path 205 isillustrated for only one set of magnets 134A, 134B, in FIG. 8; however,it is apparent that the flux path 205 is the same for all six sets ofmagnets.

[0035] Assume now that the rotor coil 124 is energized. When current isapplied to the rotor coils 124, magnetic flux 185 is generated. As shownin FIG. 8, this flux 185 flows out of pole piece 132A, through air gap144 and into stator 112. The flux 185 then flows back through air gap144 and pole piece 132B and into the inner rotor portion 123, finallyreturning to pole piece 132A and continuing the loop for as long as thecurrent remains. The current magnetic flux 185 is illustrated rotatingaround two groups of rotor coils 124, in FIG. 8, however, it is apparentthat the flux path 185 is the same for all twelve sets of rotor coils asillustrated.

[0036] With the polarities of the permanent magnets 134 and rotor coils124, as has been described, the flow of permanent magnet flux 195through poles 132A and 132B is in the opposite direction of the flux 185generated by the current in the rotor coil 124. As a result, the fluxdensity in the poles 132 and inner rotor portion 123 is reduced. Thisresults in a corresponding drop of the magnetomagnetic force in thepoles 132 and in the inner rotor portion 123. Therefore, the fluxcancellation in the poles 132 and inner rotor portion 123 results in anincrease in the flux traveling from the rotor 133 to the stator 112,which in turn increases the power output.

[0037] The permanent magnet flux 195 and current magnetic flux 185 flowas shown in FIG. 8 is similar to the permanent magnetic flux and currentmagnetic flux flow in the Lundell-type arrangement as shown in FIGS.1-5.

[0038] The present invention as described offers many advantages overprevious hybrid magnet synchronous motors, including higher output,higher efficiency, and lower magnetic noise levels.

[0039] First, because there is only one permanent magnet 134 per rotorslot 139, the present invention does not have permanent magnet fluxcancellation within the rotor slot 139 as in the '967 patent whenapplied to a salient pole synchronous machine whose rotor poles are nottapered. As such, the rotor flux associated with the permanent magnet134 is significantly increased, which in turns increases the alternator(generator) output power.

[0040] Another important feature of the present invention as describedabove is that rotor flux and hence power output is further increasedbecause the permanent magnet flux 195 in the rotor 33, 133 is againstthe flux 185 generated by the field current.

[0041] The new arrangement also lowers harmonic fluxes because thepermanent magnet flux 195 changes more gradually in the space, whichlowers the core losses caused by the harmonic flux and, therefore,raises the efficiency of the machine 100.

[0042] Further, the magnetic noise level in the first embodiment of thepresent invention as shown in FIGS. 2-4 is lower than that of the '967patent because of lower harmonic flux.

[0043] While the invention has been described in terms of preferredembodiments, it will be understood, of course, that the invention is notlimited thereto since modifications may be made by those skilled in theart, particularly in light of the foregoing teachings.

What is claimed is:
 1. A rotor for use in an electrical machine, said rotor having an axis of rotation and comprising: a first pole piece having a plurality of axially-extending first pole fingers and a first inner rotor portion; a second pole piece having a plurality of axially-extending second pole fingers and a second inner rotor portion; a field coil magnetically coupled with said first pole piece and said second pole piece which when energized magnetizes said first pole fingers and said second pole fingers such that said first pole fingers have a north magnetic polarity and said second pole fingers have a south magnetic polarity; a plurality of permanent magnets having a first set of permanent magnets and a second set of permanent magnets; one of said first set of permanent magnets disposed between one of said plurality of first pole fingers and one of said plurality of second pole fingers, said one of said first set of permanent magnets having a first radially-inward surface, a first radially-outward surface, a first side surface and a second side surface, wherein said first side surface is adjacent to one of said plurality of first pole fingers and substantially extends the length of one of said plurality of first pole fingers, wherein said second surface is adjacent to one of said plurality of second pole fingers and substantially extends the length of one of said plurality of second pole fingers; one of said second set of permanent magnets disposed between one of said plurality of first pole fingers and the other of said two adjacent said plurality of second pole fingers and having a second radially-inward surface, a second radially-outward surface, a third side surface and a fourth side surface, wherein said third side surface is adjacent to said first pole finger and substantially extends the length of said first pole finger, wherein said fourth side surface is adjacent to said other of said two adjacent said plurality of second pole fingers and substantially extends the length of said other of said two adjacent said plurality of second pole fingers; and wherein said first radially-outward surface and said first side surface have a north magnetic polarity and wherein said second radially-outward surface and said fourth side surface have a south magnetic polarity.
 2. An electrical machine having a rotor as defined in claim
 1. 3. An electrical machine having a rotor according to claim 2, wherein said electrical machine is an alternator.
 4. The electrical machine having a rotor as in claim 2, wherein said plurality of permanent magnets produces permanent magnetic flux from one of said first set of permanent magnets to each of said second set of permanent magnets located adjacent to said one of said first set of permanent magnets such that said permanent magnet flux creates a flux linkage in a stator winding on the electrical machine.
 5. The electrical machine of claim 2, wherein said plurality of permanent magnets produces permanent magnetic flux from said one of said first set of permanent magnets to one of said second set of permanent magnets located adjacent to said one of said plurality of permanent magnets such that said magnetic flux acts in opposition to a field current flux in said first pole piece and said second pole piece, whereby said flux linkage is increased in a stator winding of the electrical machine, thereby increasing output power from said stator winding of the electrical machine.
 6. The electrical machine of claim 2, wherein said plurality of permanent magnets produces permanent magnetic flux from one of said first set of permanent magnets to one of said second set of permanent magnets located adjacent to said one of said plurality of permanent magnets such that said permanent magnet flux creates a flux linkage in a stator winding on the electrical machine; and wherein said magnetic flux acts in opposition to a field current flux in said first pole piece and said second pole piece, whereby said flux linkage is increased in a stator winding of the electrical machine, thereby increasing output power from said stator winding of the electrical machine.
 7. The electrical machine of claim 1, wherein each of said plurality of permanent magnets is affixed to the rotor between one of said plurality of first pole fingers and one of said plurality of second pole fingers.
 8. A rotor for use in an electrical machine, said rotor having an axis of rotation and comprising: a plurality of axially-extending pole pieces having an inner rotor portion; a plurality of rotor coils, one of said plurality of rotor coils magnetically coupled with one of said plurality of axially-extending pole pieces which when energized magnetizes said one of said plurality of axially-extending pole pieces such that each adjacent one of said plurality of axially-extending pole piece has an opposite magnetic polarity; a plurality of permanent magnets having a first set of permanent magnets and a second set of permanent magnets; one of said first set of permanent magnets disposed between a first adjacent pair of said plurality of axially-extending pole pieces and having a first radially-inward surface, a first radially-outward surface, a first side surface and a second side surface, wherein said first side surface is adjacent to one of said first adjacent pair of pole pieces and extends the length of one of said first adjacent pair of pole pieces, wherein said second surface is adjacent to the other of said first adjacent pair of pole pieces and extends the length of other of said first adjacent pair of pole pieces; one of said second set of permanent magnets disposed between a second adjacent pair of said plurality of axially-extending pole pieces and having a second radially-inward surface, a second radially-outward surface, a third side surface and a fourth side surface, wherein said third side surface is adjacent to one of said second adjacent pair of axially-extending pole pieces and extends the length of one of said second adjacent pair of axially-extending pole pieces, wherein said fourth surface is adjacent to the other of said second adjacent pair of axially-extending pole pieces and extends the length of said other of said second adjacent pair of axially-extending pieces; wherein said other of said first adjacent pair of said plurality of axially-extending pole pieces and said other of said second adjacent pair of said plurality of axially-extending pole pieces have the same magnetic polarity ; and wherein said first radially-outward surface and said first side surface have a north magnetic polarity and wherein said second radially-outward surface and said fourth side surface have a south magnetic polarity.
 9. An electrical machine having a rotor as defined in claim
 8. 10. An electrical machine having a rotor according to claim 9, wherein said electrical machine is an alternator.
 11. The electrical machine having a rotor as in claim 9, wherein said plurality of permanent magnets produces permanent magnetic flux from said first set of permanent magnets to one of said second set of permanent magnets located adjacent to said one of said first set of permanent magnets such that said permanent magnet flux creates a flux linkage in a stator winding on the electrical machine.
 12. The electrical machine of claim 9, wherein said plurality of permanent magnets produces permanent magnetic flux from one of said first set of permanent magnets to one of said second set of permanent magnets located adjacent to said one of said first set of permanent magnets such that said magnetic flux acts in opposition to a field current flux in said plurality of axially-extending pole pieces, whereby a flux linkage is increased in a stator winding of the electrical machine, thereby increasing output power from said stator winding on the electrical machine.
 13. The electrical machine of claim 9, wherein said plurality of permanent magnets produces permanent magnetic flux from one of said first set of permanent magnets to one of said second set of permanent magnets located adjacent to said one of said first set of permanent magnets such that said permanent magnet flux creates a flux linkage in a stator winding on the electrical machine, thereby increasing output power from a stator winding on the electrical machine; and wherein said magnetic flux acts in opposition to a field current flux in said plurality of axially-extending pole pieces, whereby said flux linkage is increased in said stator winding of the electrical machine, thereby increasing output power from said stator winding on the electrical machine.
 14. The electrical machine of claim 8, wherein each of said plurality of permanent magnets is affixed to the rotor between an adjacent pair of said axially-extending pole pieces.
 15. A method of increasing rotor flux and power output in a hybrid permanent magnet synchronous machine, the method comprising the step of: generating a permanent magnet flux circulating from one of a first set of permanent magnets through a stator to one of a second set of permanent magnets, said permanent magnet flux continuing from said one of said second set of permanent magnets through one of a first set of poles, an inner rotor portion, and one of a second set of poles, thereby returning to said one of said first set of permanent magnets, wherein said permanent magnet flux in said first set of poles and said second set of poles and said inner rotor portion acts in opposition to a field current magnetic flux generated when a field winding is excited with current.
 16. A method according to claim 15, wherein the step of generating a permanent magnet flux comprises the steps of: disposing a first permanent magnet having a first radially-inward surface, a first radially-outward surface, a first side surface and a second side surface between one of said first set of poles and an adjacent one of said second set of poles, wherein said first radially-outward surface and said first side surface have a first magnetic polarity; and disposing a second permanent magnet having a second radially-inward surface, a second radially-outward surface, a third side surface and a fourth side surface between said one of said first set of poles and the other adjacent one of said second set of poles, wherein said first side surface substantially extends the length of said one of said first set of poles and is located adjacent to said adjacent one of said first set of poles and wherein said third side surface substantially extends the length of said one of said first poles and is located adjacent to said adjacent one of said first poles, wherein said second radially-outward surface and said fourth side surface have a second magnetic polarity, where said first magnetic polarity and said second magnetic polarity are opposite magnetic polarities.
 17. The method according to claim 15, wherein the step of generating a permanent magnet flux comprises the step of generating a permanent magnet flux circulating from one of a first set of permanent magnets through a stator to one of a second set of permanent magnets, said permanent magnet flux continuing from said one of said second set of permanent magnets through one of a first set of poles, an inner rotor portion, and one of a second set of poles, thereby returning to said one of said first set of permanent magnets, wherein said permanent magnet flux said first set of poles and said second set of poles and said inner rotor portion acts in opposition to a field current magnetic flux generated when a field coil is excited with current.
 18. The method according to claim 15, wherein the step of generating a permanent magnet flux comprises the step of generating a permanent magnet flux circulating from one of a first set of permanent magnets through a stator to one of a second set of permanent magnets, said permanent magnet flux continuing from said one of said second set of permanent magnets through one of a first set of poles, an inner rotor portion, and one of a second set of poles, thereby returning to said one of said first set of permanent magnets, wherein said permanent magnet flux in said first set of poles and said second set of poles and said inner portion acts in opposition to a field current magnetic flux generated when a rotor coil is excited with current. 